Suction boxes and the like have long been in use, especially in the textile industry, for extracting liquid as from a moving web. The prior art includes U.S. Pat. No. 3,836,428 which illustrates the use of polyethylene material and means for varying the widths of slots which includes top wear surfaces in the form of replaceable strips. Applicant's invention on the other hand, is concerned with the provision of means for reducing suction requirements through varying the effective length of slot to accommodate the web. Since the fabric passing over a suction slot typically wanders or drifts from side to side in the course of such passage, and since it is necessary that suction be applied across the entire width of the fabric, the slot must be of greater length than that of the cloth to accommodate such wandering.
The prior art also contemplates a blocking means for varying the effective length of a suction slot wherein a strip is unrolled to cover end portions of the slot, however, the rolling and unrolling of the blocking strip is difficult and ineffective in practice.
Accordingly, it is an important object of this invention to provide inserts moved in and out adjacent end portions of the slot generally following movement of the web from side to side so as to cover portions of the slot which are exposed by such movement. By thus blocking uncovered portions of the slot, the amount of suction necessary to remove a given quantity of liquid from the web is minimized. It is also possible in accordance with the invention, to easily accommodate various widths of cloth for use on the apparatus.
Another important object of the invention is to provide an improved suction slot with blocking means to vary the effective length thereof by moving in and out and being constructed of ultra high molecular weight polyethylene so that the Durometer hardness of the insert is less than that of the wear surface.
Another important object of the invention is the provision of apparatus for treating a web wherein tracking means are provided for following the side to side movements of the web which include inner and outer sensing means positioned on each side of the web which move responsive to movement of the web. Such sensing means also move the blocking means hereof.